Rack base



FIG. 1 is a perspective view of the rack base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view of the design in state of use.

The broken lines are for illustrating environment structure only and form no part of the claimed design. 

CLAIM The ornamental design for a rack base, as shown and described. 